The phenomenon of resonance is something known about for thousands of years. It is often only partially understood, confused with episodes of mystical philosophy. We find traces of it in ancient writes and in the oral tradition, but also in ancient artifacts and prehistoric architecture. Armed with this background and previous experience we opted to study the Ravne tunnels (Visoko, Bosnia-Herzegovina). These were considered by some to be very old mines perhaps of the Neolithic period, but without valuing it as a very special temple, where ceremonies could have taken place. Sound examination was immediately possible to verify a response sound resonance at very low frequencies, which lasted up to 20 seconds after the end of harmonic singing. The sound response of the tunnel was approximately 74 Hz, showing the shape of a wave similar to a Gaussian curve easily excited by the singers. The experience lasted several hours and was always repeated at the right vocal strain, confirming the repeatability of the phenomenon on equal terms.
Although only preliminary, the examination carried out shows it would appear difficult to achieve a similar sound in a structure whose path is just random as is typical of a mine. The duration of the phenomenon does not appear typical of an echo or a reverberation. Rather it is more typical of a resonance phenomenon evidently sought through a link between the structure and the human voice. Further research is necessary using sound generators (electronic oscillators) that are able to resonate with the exact structure. An operation that we hope to undertake in the coming months.
